DESCRIPTION(Adapted from applicant's abstract): Although recent studies have revealed a great deal about the molecular basis of drug addiction, numerous gaps remain in our understanding of the changes in gene expression that are associated with chronic drug intake. One prominent alteration that occurs upon chronic cocaine exposure is accumulation in the striatum of very stable isoforms of the transcription factor deltaFosB that is produced by alternative splicing of the fosB transcript. The deltaFosB isoforms may mediate some of the neural and behavioral modivications that occur with drug addiction. The factors that play a role in the alternative splicing of deltaFasB have not yet been identified. To begin to understand the posttranscriptional events that lead to the production of stable deltaFosB, we will test the hypothesis that both cis- and trans-acting factors are important in this regulation. To test this hypothesis, mutation analysis of fosB will be used to identify the sequences essential for pre-mRNA splicing. Cross linking and RNA binding studies will be undertaken to determine which trans acting factors bind to the RNA in splicing extracts prepared from brains. Factors identified in these studies will be tested in splicing assays to determine if they regulate splicing invitro. These studies will identify the factors required for the regulation of splicing during chronic- cocaine use and lead to an understanding of the mechanisms involved. Because deltaFosB is also induced by chronic administration of other drugs of abuse, such as amphetamine, nicotine and opiates, the results obtained in this study may also lead to a better understanding of drug addiction.